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MongoDB Tutorial

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MONGODB TUTORIAL

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ABOUT THE TUTORIAL

MongoDb tutorial

MongoDB is an open-source document database, and leading NoSQL database. MongoDB is written in c++.

This tutorial will give you great understanding on MongoDB concepts needed to create and deploy a highly scalable and performance oriented database.

Audience

This tutorial is designed for Software Professionals who are willing to learn MongoDB Database in simple and easy steps. This tutorial will give you great understanding on MongoDB concepts and after completing this tutorial you will be at intermediate level of expertise from where you can take yourself at higher level of expertise.

Prerequisites

Before proceeding with this tutorial you should have a basic understanding of database, text editor and execution of programs etc. Because we are going to develop high performance database, so it will be good if you have understanding on basic concepts of Database (RDBMS).

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Table of Content

MongoDb tutorial ...................................................................... 1

Audience .................................................................................. 1

Prerequisites ............................................................................ 1

MongoDB Overview ................................................................. 6 Database ................................................................................. 6 Collection ................................................................................. 6 Document ................................................................................ 6 Sample document .................................................................... 7

MongoDB Advantages ............................................................. 8 Advantages of MongoDB over RDBMS .................................... 8 Why should use MongoDB ....................................................... 8 Where should use MongoDB? ................................................. 8

MongoDB Environment ............................................................ 9 Install MongoDB On Windows .................................................. 9 Install MongoDB on Ubuntu ................................................... 10 MongoDB Help ....................................................................... 11 MongoDB Statistics ................................................................ 12

MongoDB Data Modelling ...................................................... 13 Some considerations while designing schema in MongoDB ... 13 Example ................................................................................. 13

MongoDB Create Database ................................................... 15 The use Command ................................................................ 15 Syntax: ................................................................................... 15 Example: ................................................................................ 15

MongoDB Drop Database ...................................................... 16 The dropDatabase () Method ................................................. 16 Syntax: ................................................................................... 16 Example: ................................................................................ 16

MongoDB Create Collection ................................................... 17 The createCollection() Method ............................................... 17 Syntax: ................................................................................... 17 Examples: .............................................................................. 18

MongoDB Drop Collection ...................................................... 19 The drop() Method ................................................................. 19 Syntax: ................................................................................... 19 Example: ................................................................................ 19

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MongoDB Datatypes .............................................................. 20

MongoDB - Insert Document .................................................. 21 The insert() Method ................................................................ 21 Syntax .................................................................................... 21 Example ................................................................................. 21 Example ................................................................................. 21

MongoDB - Query Document ................................................. 23 The find() Method ................................................................... 23 Syntax .................................................................................... 23 The pretty() Method ............................................................... 23 Syntax: ................................................................................... 23 Example ................................................................................. 23 RDBMS Where Clause Equivalents in MongoDB ................... 24 AND in MongoDB ................................................................... 24 Syntax: ................................................................................... 24 Example ................................................................................. 24 OR in MongoDB ..................................................................... 25 Syntax: ................................................................................... 25 Example ................................................................................. 25 Using AND and OR together .................................................. 26 Example ................................................................................. 26

MongoDB Update Document ................................................. 27 MongoDB Update() method ................................................... 27 Syntax: ................................................................................... 27 Example ................................................................................. 27 MongoDB Save() Method ....................................................... 28 Syntax .................................................................................... 28 Example ................................................................................. 28

MongoDB Delete Document .................................................. 29 The remove() Method............................................................. 29 Syntax: ................................................................................... 29

Example ................................................................................. 29

Remove only one ................................................................... 29

Remove All documents .......................................................... 29

MongoDB Projection .............................................................. 30

The find() Method ................................................................... 30

Syntax: ................................................................................... 30

Example ................................................................................. 30

MongoDB Limit Records ........................................................ 31

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The Limit() Method ................................................................. 31

Syntax: ................................................................................... 31

Example ................................................................................. 31

MongoDB Skip() Method ........................................................ 31

Syntax: ................................................................................... 31

Example: ................................................................................ 31

MongoDB Sort Documents .................................................... 32

The sort() Method .................................................................. 32

Syntax: ................................................................................... 32

Example ................................................................................. 32

MongoDB Indexing ................................................................ 33

The ensureIndex() Method ..................................................... 33

Syntax: ................................................................................... 33

Example ................................................................................. 33

MongoDB Aggregation ........................................................... 35

The aggregate() Method ........................................................ 35

Syntax: ................................................................................... 35

Example: ................................................................................ 35

Pipeline Concept .................................................................... 37

MongoDB Replication ............................................................ 38

Why Replication? ................................................................... 38

How replication works in MongoDB ........................................ 38

Replica set features ............................................................... 39

Set up a replica set ................................................................ 39

Example ................................................................................. 39

Add members to replica set ................................................... 40

Synttax: .................................................................................. 40

Example ................................................................................. 40

MongoDB Sharding ................................................................ 41

Sharding ................................................................................ 41

Why Sharding? ...................................................................... 41

Sharding in MongoDB ............................................................ 41

MongoDB Create Backup ...................................................... 43

Dump MongoDB Data ............................................................ 43

Syntax: ................................................................................... 43

Example ................................................................................. 43

Restore data .......................................................................... 44

Syntax .................................................................................... 44

MongoDB Deployment ........................................................... 45

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mongostat .............................................................................. 45

mongotop ............................................................................... 46

MongoDB Java ...................................................................... 48

Installation .............................................................................. 48

Connect to database .............................................................. 48

Create a collection ................................................................. 49

Getting/ selecting a collection................................................. 50

Insert a document .................................................................. 51

Retrieve all documents ........................................................... 52

Update document ................................................................... 53

Delete first document ............................................................. 55

MongoDB PHP ....................................................................... 57

Make a connection and Select a database ............................. 57

Create a collection ................................................................. 57

Insert a document .................................................................. 58

Find all documents ................................................................. 59

Update a document ................................................................ 59

Delete a document ................................................................. 60

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MongoDB Overview

MongoDB is a cross-platform, document oriented database that provides, high performance, high availability,

and easy scalability. MongoDB works on concept of collection and document.

Database Database is a physical container for collections. Each database gets its own set of files on the file system. A single MongoDB server typically has multiple databases.

Collection Collection is a group of MongoDB documents. It is the equivalent of an RDBMS table. A collection exists within a single database. Collections do not enforce a schema. Documents within a collection can have different fields. Typically, all documents in a collection are of similar or related purpose.

Document A document is a set of key-value pairs. Documents have dynamic schema. Dynamic schema means that documents in the same collection do not need to have the same set of fields or structure, and common fields in a collection's documents may hold different types of data.

Below given table shows the relationship of RDBMS terminology with MongoDB

RDBMS MongoDB

Database Database

Table Collection

Tuple/Row Document

column Field

Table Join Embedded Documents

Primary Key Primary Key (Default key _id provided by mongodb

itself)

Database Server and Client

Mysqld/Oracle mongod

mysql/sqlplus mongo

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Sample document Below given example shows the document structure of a blog site which is simply a comma separated key value pair.

{

_id: ObjectId(7df78ad8902c)

title: 'MongoDB Overview',

description: 'MongoDB is no sql database',

by: 'tutorials point',

url: 'http://www.tutorialspoint.com',

tags: ['mongodb', 'database', 'NoSQL'],

likes: 100,

comments: [ { user:'user1',

message: 'My first comment',

dateCreated: new Date(2011,1,20,2,15),

like: 0 },

{ user:'user2',

message: 'My second comments',


like: 5 } ] }

_id is a 12 bytes hexadecimal number which assures the uniqueness of every document. You can provide _id

while inserting the document. If you didn't provide then MongoDB provide a unique id for every document. These 12 bytes first 4 bytes for the current timestamp, next 3 bytes for machine id, next 2 bytes for process id of mongodb server and remaining 3 bytes are simple incremental value.

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MongoDB Advantages

Any relational database has a typical schema design that shows number of tables and the relationship between

these tables. While in MongoDB there is no concept of relationship

Advantages of MongoDB over RDBMS Schema less : MongoDB is document database in which one collection holds different different documents.

Number of fields, content and size of the document can be differ from one document to another.

Structure of a single object is clear

No complex joins

Deep query-ability. MongoDB supports dynamic queries on documents using a document-based query language

that's nearly as powerful as SQL

Tuning

Ease of scale-out: MongoDB is easy to scale

Conversion / mapping of application objects to database objects not needed

Uses internal memory for storing the (windowed) working set, enabling faster access of data

Why should use MongoDB Document Oriented Storage : Data is stored in the form of JSON style documents

Index on any attribute

Replication & High Availability

Auto-Sharding

Rich Queries

Fast In-Place Updates

Professional Support By MongoDB

Where should use MongoDB?

Big Data

Content Management and Delivery

Mobile and Social Infrastructure

User Data Management

Data Hub

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MongoDB Environment

Install MongoDB On Windows To install the MongoDB on windows, first doownload the latest release of MongoDB from http://www.mongodb.org/downloads Make sure you get correct version of MongoDB depending upon your windows version. To get your windows version open command prompt and execute following command

C:\>wmic os get osarchitecture

OSArchitecture

64-bit

C:\>

32-bit versions of MongoDB only support databases smaller than 2GB and suitable only for testing and evaluation purposes.

Now extract your downloaded file to c:\ drive or any other location. Make sure name of the extracted folder is mongodb-win32-i386-[version] or mongodb-win32-x86_64-[version]. Here [version] is the version of MongoDB download.

Now open command prompt and run the following command

C:\>move mongodb-win64-* mongodb

1 dir(s) moved.

C:\>

In case you have extracted the mondodb at different location, then go to that path by using command cd FOOLDER/DIR and now run the above given process.

MongoDB requires a data folder to store its files. The default location for the MongoDB data directory is c:\data\db. So you need to create this folder using the Command Prompt. Execute the following command sequence

C:\>md data

C:\md data\db

If you have install the MongoDB at different location, then you need to specify any alternate path for \data\db by

setting the path dbpath in mongod.exe. For the same issue following commands

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http://www.mongodb.org/downloads

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In command prompt navigate to the bin directory present into the mongodb installation folder. Suppose my installation folder is D:\set up\mongodb

C:\Users\XYZ>d:

D:\>cd "set up"

D:\set up>cd mongodb

D:\set up\mongodb>cd bin

D:\set up\mongodb\bin>mongod.exe --dbpath "d:\set up\mongodb\data"

This will show waiting for connections message on the console output indicates that the mongod.exe process is

running successfully.

Now to run the mongodb you need to open another command prompt and issue the following command

D:\set up\mongodb\bin>mongo.exe

MongoDB shell version: 2.4.6

connecting to: test

>db.test.save( { a: 1 } )

>db.test.find()

{ "_id" : ObjectId(5879b0f65a56a454), "a" : 1 }

>

This will show that mongodb is installed and run successfully. Next time when you run mongodb you need to issue only commands

D:\set up\mongodb\bin>mongod.exe --dbpath "d:\set up\mongodb\data"

D:\set up\mongodb\bin>mongo.exe

Install MongoDB on Ubuntu Run the following command to import the MongoDB public GPG Key:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10

Create a /etc/apt/sources.list.d/mongodb.list file using the following command.

echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | sudo tee /etc/apt/sources.list.d/mongodb.list

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Now issue the following command to update the repository:

sudo apt-get update

Now install the MongoDB by using following command:

apt-get install mongodb-10gen=2.2.3

In the above installation 2.2.3 is currently released mongodb version. Make sure to install latest version always. Now mongodb is installed successfully.

Start MongoDB

sudo service mongodb start

Stop MongoDB

sudo service mongodb stop

Restart MongoDB

sudo service mongodb restart

To use mongodb run the following command

mongo

This will connect you to running mongod instance.

MongoDB Help To get list of commands type db.help() in mongodb client. This will give you list of commands as follows:

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MongoDB Statistics To get stats about mongodb server type the command db.stats() in mongodb client. This will show the database

name, cumber of collection and documents in the database. Output the command is shown below:

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MongoDB Data Modelling

Data in MongoDB has a flexible schema.documents in the same collection do not need to have the same set of

fields or structure, and common fields in a collection’s documents may hold different types of data.

Some considerations while designing schema in MongoDB Design your schema according to user requirements.

Combine objects into one document if you will use them together. Otherwise separate them (but make sure there

should not be need of joins).

Duplicate the data (but limited) because disk space is cheap as compare to compute time.

Do joins while write, not on read.

Optimize your schema for most frequent use cases.

Do complex aggregation in the schema

Example Suppose a client needs a database design for his blog website and see the differences between RDBMS and MongoDB schema design. Website has the following requirements.

Every post has the unique title, description and url.

Every post can have one or more tags.

Every post has the name of its publisher and total number of likes.

Every Post have comments given by users along with their name, message, data-time and likes.

On each post there can be zero or more comments.

In RDBMS schema design for above requirements will have minimum three tables.

While in MongoDB schema design will have one collection post and has the following structure:

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{

_id: POST_ID

title: TITLE_OF_POST,

description: POST_DESCRIPTION,

by: POST_BY,

url: URL_OF_POST,

tags: [TAG1, TAG2, TAG3],

likes: TOTAL_LIKES,

comments: [

{

user:'COMMENT_BY',

message: TEXT,

dateCreated: DATE_TIME,

like: LIKES

},

{

user:'COMMENT_BY',

message: TEXT,

dateCreated: DATE_TIME,

like: LIKES

}

]

}

So while showing the data, in RDBMS you need to join three tables and in mongodb data will be shown from one collection only.

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MongoDB Create Database

The use Command MongoDB use DATABASE_NAME is used to create database. The command will create a new database, if it

doesn't exist otherwise it will return the existing database.

Syntax:

Basic syntax of use DATABASE statement is as follows:

use DATABASE_NAME

Example:

If you want to create a database with name <mydb>, then use DATABASE statement would be as follows:

>use mydb

switched to db mydb

To check your currently selected database use the command db

>db

mydb

If you want to check your databases list, then use the command show dbs.

>show dbs

local 0.78125GB

test 0.23012GB

Your created database (mydb) is not present in list. To display database you need to insert atleast one document into it.

>db.movie.insert({"name":"tutorials point"})

>show dbs

local 0.78125GB

mydb 0.23012GB

test 0.23012GB

In mongodb default database is test. If you didn't create any database then collections will be stored in test database.

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MongoDB Drop Database

The dropDatabase () Method MongoDB db.dropDatabase () command is used to drop a existing database.

Syntax:

Basic syn tax of dropDatabase () command is as follows:

db.dropDatabase()

This will delete the selected database. If you have not selected any database, then it will delete default 'test' database

Example:

First, check the list available databases by using the command show dbs

>show dbs

local 0.78125GB

mydb 0.23012GB

test 0.23012GB

>

If you want to delete new database <mydb>, then dropDatabase() command would be as follows:

>use mydb

switched to db mydb

>db.dropDatabase()

>{ "dropped" : "mydb", "ok" : 1 }

>

Now check list of databases

>show dbs

local 0.78125GB

test 0.23012GB

>

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MongoDB Create Collection

The createCollection() Method MongoDB db.createCollection(name, options) is used to create collection.

Syntax:

Basic syntax of createCollection() command is as follows

db.createCollection(name, options)

In the command, name is name of collection to be created. Options is a document and used to specify configuration

of collection

Parameter Type Description

Name String Name of the collection to be created

Options Document (Optional) Specify options about memory size and indexing

Options parameter is optional, so you need to specify only name of the collection. Following is the list of options you can use:

Field Type Description

capped Boolean

(Optional) If true, enables a capped collection. Capped collection is a collection fixed size collecction that automatically overwrites its oldest entries when it reaches its maximum size. If you specify true, you need to specify size parameter also.

autoIndexID Boolean (Optional) If true, automatically create index on _id field.s

Default value is false.

size number (Optional) Specifies a maximum size in bytes for a capped

collection. If If capped is true, then you need to specify this field also.

max number (Optional) Specifies the maximum number of documents

allowed in the capped collection.

While inserting the document, MongoDB first checks size field of capped collection, then it checks max field.

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Examples:

Basic syntax of createCollection() method without options is as follows

>use test

switched to db test

>db.createCollection("mycollection")

{ "ok" : 1 }

>

You can check the created collection by using the command show collections

>show collections

mycollection

system.indexes

Following example shows the syntax of createCollection() method with few important options:

>db.createCollection("mycol", { capped : true, autoIndexID : true, size : 6142800, max : 10000 } )

{ "ok" : 1 }

>

In mongodb you don't need to create collection. MongoDB creates collection automatically, when you insert some document.

>db.tutorialspoint.insert({"name" : "tutorialspoint"})

>show collections

mycol

mycollection

system.indexes

tutorialspoint

>

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MongoDB Drop Collection

The drop() Method MongoDB's db.collection.drop() is used to drop a collection from the database.

Syntax:

Basic syntax of drop() command is as follows

db.COLLECTION_NAME.drop()

Example:

First, check the available collections into your database mydb

>use mydb

switched to db mydb

>show collections

mycol

mycollection

system.indexes

tutorialspoint

>

Now drop the collection with the name mycollection

>db.mycollection.drop()

true

>

Again check the list of collections into database

>show collections

mycol

system.indexes

tutorialspoint

>

drop() method will return true, if the selected collection is dropped successfully otherwise it will return false

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MongoDB Datatypes

MongoDB supports many datatypes whose list is given below:

String : This is most commonly used datatype to store the data. String in mongodb must be UTF-8 valid.

Integer : This type is used to store a numerical value. Integer can be 32 bit or 64 bit depending upon your server.

Boolean : This type is used to store a boolean (true/ false) value.

Double : This type is used to store floating point values.

Min/ Max keys : This type is used to compare a value against the lowest and highest BSON elements.

Arrays : This type is used to store arrays or list or multiple values into one key.

Timestamp : ctimestamp. This can be handy for recording when a document has been modified or added.

Object : This datatype is used for embedded documents.

Null : This type is used to store a Null value.

Symbol : This datatype is used identically to a string however, it's generally reserved for languages that use a

specific symbol type.

Date : This datatype is used to store the current date or time in UNIX time format. You can specify your own date

time by creating object of Date and passing day, month, year into it.

Object ID : This datatype is used to store the document’s ID.

Binary data : This datatype is used to store binay data.

Code : This datatype is used to store javascript code into document.

Regular expression : This datatype is used to store regular expression

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MongoDB - Insert Document

The insert() Method To insert data into MongoDB collection, you need to use MongoDB's insert() or save()method.

Syntax

Basic syntax of insert() command is as follows:

>db.COLLECTION_NAME.insert(document)

Example

>db.mycol.insert({

_id: ObjectId(7df78ad8902c),






likes: 100

})

Here mycol is our collection name, as created in previous tutorial. If the collection doesn't exist in the database, then

MongoDB will create this collection and then insert document into it.

In the inserted document if we don't specify the _id parameter, then MongoDB assigns an unique ObjectId for this document.

_id is 12 bytes hexadecimal number unique for every document in a collection. 12 bytes are divided as follows:

_id: ObjectId(4 bytes timestamp, 3 bytes machine id, 2 bytes process id, 3 bytes incrementer)

To insert multiple documents in single query, you can pass an array of documents in insert() command.

Example

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>db.post.insert([

{






likes: 100

},

{

title: 'NoSQL Database',

description: 'NoSQL database doesn't have tables',




likes: 20,

comments: [

{

user:'user1',

message: 'My first comment',


like: 0

}

]

}

])

To insert the document you can use db.post.save(document) also. If you don't specify _id in the document then save() method will work same as insert() method. If you specify _id then it will replace whole data of

document containing _id as specified in save() method.

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MongoDB - Query Document

The find() Method To query data from MongoDB collection, you need to use MongoDB's find() method.

Syntax

Basic syntax of find() method is as follows

>db.COLLECTION_NAME.find()

find() method will display all the documents in a non structured way.

The pretty() Method To display the results in a formatted way, you can use pretty() method.

Syntax:

>db.mycol.find().pretty()

Example

>db.mycol.find().pretty()

{

"_id": ObjectId(7df78ad8902c),

"title": "MongoDB Overview",

"description": "MongoDB is no sql database",

"by": "tutorials point",

"url": "http://www.tutorialspoint.com",

"tags": ["mongodb", "database", "NoSQL"],

"likes": "100"

}

>

Apart from find() method there is findOne() method, that reruns only one document.

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RDBMS Where Clause Equivalents in MongoDB To query the document on the basis of some condition, you can use following operations

Operation Syntax Example RDBMS Equivalent

Equality {<key>:<value>} db.mycol.find({"by":"tuto

rials point"}).pretty() where by =

'tutorials point'

Less Than {<key>:{$lt:<value>}} db.mycol.find({"likes":{$l

t:50}}).pretty() where likes < 50

Less Than

Equals

{<key>:{$lte:<value>}} db.mycol.find({"likes":{$l

te:50}}).pretty() where likes <=

50

Greater Than {<key>:{$gt:<value>}} db.mycol.find({"likes":{$

gt:50}}).pretty() where likes > 50

Greater Than

Equals

{<key>:{$gte:<value>}} db.mycol.find({"likes":{$

gte:50}}).pretty() where likes >=

50

Not Equals {<key>:{$ne:<value>}} db.mycol.find({"likes":{$

ne:50}}).pretty() where likes !=

50

AND in MongoDB

Syntax:

In the find() method if you pass multiple keys by separating them by ',' then MongoDB treats it AND condition. Basic syntax of AND is shown below:

>db.mycol.find({key1:value1, key2:value2}).pretty()

Example

Below given example will show all the tutorials written by 'tutorials point' and whose title is 'MongoDB Overview'

>db.mycol.find({"by":"tutorials point","title": "MongoDB Overview"}).pretty()

{







"likes": "100"

} >

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For the above given example equivalent where clause will be ' where by='tutorials point' AND title='MongoDB Overview' '. You can pass any number of key, value pairs in find clause.

OR in MongoDB

Syntax:

To query documents based on the OR condition, you need to use $or keyword. Basic syntax of OR is shown below:

>db.mycol.find(

{

$or: [

{key1: value1}, {key2:value2}

]

}

).pretty()

Example

Below given example will show all the tutorials written by 'tutorials point' or whose title is 'MongoDB Overview'

>db.mycol.find({$or:[{"by":"tutorials point"},{"title": "MongoDB Overview"}]}).pretty()

{







"likes": "100"

}

>

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Using AND and OR together

Example

Below given example will show the documents that have likes greater than 100 and whose title is either 'MongoDB Overview' or by is 'tutorials point'. Equivalent sql where clause is 'where likes>10 AND (by = 'tutorials point' OR title = 'MongoDB Overview')'

>db.mycol.find("likes": {$gt:10}, $or: [{"by": "tutorials point"}, {"title": "MongoDB Overview"}] }).pretty()

{







"likes": "100"

}

>

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MongoDB Update Document

MongoDB's update() and save() methods are used to update document into a collection. The update() method

update values in the existing document while the save() method replaces the existing document with the document passed in save() method.

MongoDB Update() method The update() method updates values in the existing document.

Syntax:

Basic syntax of update() method is as follows

>db.COLLECTION_NAME.update(SELECTIOIN_CRITERIA, UPDATED_DATA)

Example

Consider the mycol collectioin has following data.

{ "_id" : ObjectId(5983548781331adf45ec5), "title":"MongoDB Overview"}

{ "_id" : ObjectId(5983548781331adf45ec6), "title":"NoSQL Overview"}

{ "_id" : ObjectId(5983548781331adf45ec7), "title":"Tutorials Point Overview"}

Following example will set the new title 'New MongoDB Tutorial' of the documents whose title is 'MongoDB Overview'

>db.mycol.update({'title':'MongoDB Overview'},{$set:{'title':'New MongoDB Tutorial'}})

>db.mycol.find()

{ "_id" : ObjectId(5983548781331adf45ec5), "title":"New MongoDB Tutorial"}



>

By default mongodb will update only single document, to update multiple you need to set a paramter 'multi' to true.

>db.mycol.update({'title':'MongoDB Overview'},{$set:{'title':'New MongoDB Tutorial'}},{multi:true})

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MongoDB Save() Method The save() method replaces the existing document with the new document passed in save() method

Syntax

Basic syntax of mongodb save() method is shown below:

>db.COLLECTION_NAME.save({_id:ObjectId(),NEW_DATA})

Example

Following example will replace the document with the _id '5983548781331adf45ec7'

>db.mycol.save(

{

"_id" : ObjectId(5983548781331adf45ec7), "title":"Tutorials Point New Topic", "by":"Tutorials Point"

}

)

>db.mycol.find()

{ "_id" : ObjectId(5983548781331adf45ec5), "title":"Tutorials Point New Topic", "by":"Tutorials Point"}



>

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MongoDB Delete Document

The remove() Method MongoDB's remove() method is used to remove document from the collection. remove() method accepts two

parameters. One is deletion criteria and second is justOne flag

1. deletion criteria : (Optional) deletion criteria according to documents will be removed.

2. justOne : (Optional) if set to true or 1, then remove only one document.

Syntax:

Basic syntax of remove() method is as follows

>db.COLLECTION_NAME.remove(DELLETION_CRITTERIA)

Example





Following example will remove all the documents whose title is 'MongoDB Overview'

>db.mycol.remove({'title':'MongoDB Overview'})

>db.mycol.find()



>

Remove only one If there are multiple records and you want to delete only first record, then set justOne parameter in remove() method

>db.COLLECTION_NAME.remove(DELETION_CRITERIA,1)

Remove All documents If you don't specify deletion criteria, then mongodb will delete whole documents from the collection. This is equivalent of SQL's truncate command.

>db.mycol.remove()

>db.mycol.find()

>

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MongoDB Projection

In mongodb projection meaning is selecting only necessary data rather than selecting whole of the data of a

document. If a document has 5 fields and you need to show only 3, then select only 3 fields from them.

The find() Method MongoDB's find() method, explained in MongoDB Query Document accepts second optional parameter that is list of fields that you want to retrieve. In MongoDB when you execute find() method, then it displays all fields of a document.

To limit this you need to set list of fields with value 1 or 0. 1 is used to show the filed while 0 is used to hide the field.

Syntax:

Basic syntax of find() method with projection is as follows

>db.COLLECTION_NAME.find({},{KEY:1})

Example

Consider the collection myycol has the following data




Following example will display the title of the document while quering the document.

>db.mycol.find({},{"title":1,_id:0})

{"title":"MongoDB Overview"}

{"title":"NoSQL Overview"}

{"title":"Tutorials Point Overview"}

>

Please note _id field is always displayed while executing find() method, if you don't want this field, then you need to

set it as 0

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MongoDB Limit Records

The Limit() Method To limit the records in MongoDB, you need to use limit() method. limit() method accepts one number type argument,

which is number of documents that you want to displayed.

Syntax:

Basic syntax of limit() method is as follows

>db.COLLECTION_NAME.find().limit(NUMBER)

Example





Following example will display only 2 documents while quering the document.

>db.mycol.find({},{"title":1,_id:0}).limit(2)



>

If you don't specify number argument in limit() method then it will display all documents from the collection.

MongoDB Skip() Method Apart from limit() method there is one more method skip() which also accepts number type argument and used to

skip number of documents.

Syntax:

Basic syntax of skip() method is as follows

>db.COLLECTION_NAME.find().limit(NUMBER).skip(NUMBER)

Example:

Following example will only display only second document.

>db.mycol.find({},{"title":1,_id:0}).limit(1).skip(1)


>

Please note default value in skip() method is 0

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MongoDB Sort Documents

The sort() Method To sort documents in MongoDB, you need to use sort() method. sort() method accepts a document containing list of

fields along with their sorting order. To specify sorting order 1 and -1 are used. 1 is used for ascending order while -1 is used for descending order.

Syntax:

Basic syntax of sort() method is as follows

>db.COLLECTION_NAME.find().sort({KEY:1})

Example





Following example will display the documents sorted by title in descending order.

>db.mycol.find({},{"title":1,_id:0}).sort({"title":-1})

{"title":"Tutorials Point Overview"}



>

Please note if you don't specify the sorting preference, then sort() method will display documents in ascending order.

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MongoDB Indexing

Indexes support the efficient resolution of queries. Without indexes, MongoDB must scan every document of a

collection to select those documents that match the query statement. This scan is highly inefficient and require the mongod to process a large volume of data.

Indexes are special data structures, that store a small portion of the data set in an easy to traverse form. The index stores the value of a specific field or set of fields, ordered by the value of the field as specified in index.

The ensureIndex() Method To create an index you need to use ensureIndex() method of mongodb.

Syntax:

Basic syntax of ensureIndex() method is as follows()

>db.COLLECTION_NAME.ensureIndex({KEY:1})

Here key is the name of filed on which you want to create index and 1 is for ascending order. To create index in descending order you need to use -1.

Example

>db.mycol.ensureIndex({"title":1})

>

In ensureIndex() method you can pass multiple fields, to create index on multiple fields.

>db.mycol.ensureIndex({"title":1,"description":-1})

>

ensureIndex() method also accepts list of options (which are optional), whose list is given below:

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Parameter Type Description

background Boolean Builds the index in the background so that building an index does not block other database activities. Specify true to build in the background. The default value is false.

unique Boolean

Creates a unique index so that the collection will not accept insertion of documents where the index key or keys match an existing value in the index. Specify true to create a unique index. The default value is false.

name string The name of the index. If unspecified, MongoDB generates an index name by concatenating the names of the indexed fields and the sort order.

dropDups Boolean

Creates a unique index on a field that may have duplicates. MongoDB indexes only the first occurrence of a key and removes all documents from the collection that contain subsequent occurrences of that key. Specify true to create unique index. The default value is false.

sparse Boolean

If true, the index only references documents with the specified field. These indexes use less space but behave differently in some situations (particularly sorts). The default value is false.

expireAfterSeconds integer Specifies a value, in seconds, as a TTL to control how long MongoDB retains documents in this collection.

v index version

The index version number. The default index version depends on the version of mongod running when creating the index.

weights document The weight is a number ranging from 1 to 99,999 and denotes the significance of the field relative to the other indexed fields in terms of the score.

default_language string For a text index, the language that determines the list of stop words and the rules for the stemmer and tokenizer. The default value is english.

language_override string For a text index, specify the name of the field in the document that contains, the language to override the default language. The default value is language.

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MongoDB Aggregation

Aggregations operations process data records and return computed results. Aggregation operations group

values from multiple documents together, and can perform a variety of operations on the grouped data to return a single result. In sql count(*) and with group by is an equivalent of mongodb aggregation.

The aggregate() Method For the aggregation in mongodb you should use aggregate() method.

Syntax:

Basic syntax of aggregate() method is as follows

>db.COLLECTION_NAME.aggregate(AGGREGATE_OPERATION)

Example:

In the collection you have the following data:

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{

_id: ObjectId(7df78ad8902c)



by_user: 'tutorials point',



likes: 100

},

{

_id: ObjectId(7df78ad8902d)

title: 'NoSQL Overview',

description: 'No sql database is very fast',

by_user: 'tutorials point',



likes: 10

},

{

_id: ObjectId(7df78ad8902e)

title: 'Neo4j Overview',

description: 'Neo4j is no sql database',

by_user: 'Neo4j',

url: 'http://www.neo4j.com',

tags: ['neo4j', 'database', 'NoSQL'],

likes: 750

},

Now from the above collection if you want to display a list that how many tutorials are written by each user then you will use aggregate() method as shown below:

> db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$sum : 1}}}])

{

"result" : [

{

"_id" : "tutorials point",

"num_tutorial" : 2

},

{

"_id" : "tutorials point",

"num_tutorial" : 1

}

],

"ok" : 1

}

>

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Sql equivalent query for the above use case will be select by_user, count(*) from mycol group by by_user

In the above example we have grouped documents by field by_user and on each occurance of by_user previous

value of sum is incremented. There is a list available aggregation expressions .

Expression Description Example

$sum Sums up the defined value from all documents in the collection.

db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$sum : "$likes"}}}])

$avg Calculates the average of all given values from all documents in the collection.

db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$avg : "$likes"}}}])

$min Gets the minimum of the corresponding values from all documents in the collection.

db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$min : "$likes"}}}])

$max Gets the maximum of the corresponding values from all documents in the collection.

db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$max : "$likes"}}}])

$push Inserts the value to an array in the resulting document. db.mycol.aggregate([{$group : {_id : "$by_user", url : {$push: "$url"}}}])

$addToSet Inserts the value to an array in the resulting document but does not create duplicates.

db.mycol.aggregate([{$group : {_id : "$by_user", url : {$addToSet : "$url"}}}])

$first

Gets the first document from the source documents according to the grouping. Typically this makes only sense together with some previously applied “$sort”-stage.

db.mycol.aggregate([{$group : {_id : "$by_user", first_url : {$first : "$url"}}}])

$last

Gets the last document from the source documents according to the grouping. Typically this makes only sense together with some previously applied “$sort”-stage.

db.mycol.aggregate([{$group : {_id : "$by_user", last_url : {$last : "$url"}}}])

Pipeline Concept In UNIX command shell pipeline means the possibility to execute an operation on some input and use the output as the input for the next command and so on. MongoDB also support same concept in aggregation framework. There is a set of possible stages and each of those is taken a set of documents as an input and is producing a resulting set of documents (or the final resulting JSON document at the end of the pipeline). This can then in turn again be used for the next stage an so on.

Possible stages in aggregation framework are following:

$project: Used to select some specific fields from a collection.

$match: This is a filtering operation and thus this can reduce the amount of documents that are given as input to

the next stage.

$group: This does the actual aggregation as discussed above.

$sort: Sorts the documents.

$skip: With this it is possible to skip forward in the list of documents for a given amount of documents.

$limit: This limits the amount of documents to look at by the given number starting from the current position.s

$unwind: This is used to unwind document that are using arrays. when using an array the data is kind of pre-

joinded and this operation will be undone with this to have individual documents again. Thus with this stage we will increase the amount of documents for the next stage.

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MongoDB Replication

Replication is the process of synchronizing data across multiple servers. Replication provides redundancy and

increases data availability with multiple copies of data on different database servers, replication protects a database from the loss of a single server. Replication also allows you to recover from hardware failure and service interruptions. With additional copies of the data, you can dedicate one to disaster recovery, reporting, or backup.

Why Replication? To keep your data safe

High (24*7) availability of data

Disaster Recovery

No downtime for maintenance (like backups, index rebuilds, compaction)

Read scaling (extra copies to read from)

Replica set is transparent to the application

How replication works in MongoDB MongoDB achieves replication by the use of replica set. A replica set is a group of mongod instances that host the

same data set. In a replica one node is primary node that receives all write operations. All other instances, secondaries, apply operations from the primary so that they have the same data set. Replica set can have only one primary node.

1. Replica set is a group of two or more nodes (generally minimum 3 nodes are required).

2. In a replica set one node is primary node and remaining nodes are secondary.

3. All data replicates from primary to secondary node.

4. At the time of automatic failover or maintenance, election establishes for primary and a new primary node is elected.

5. After the recovery of failed node, it again join the replica set and works as a secondary node.

A typical diagram of mongodb replication is shown in which client application always interact with primary node and primary node then replicate the data to the secondary nodes.

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Replica set features A cluster of N nodess

Anyone node can be primary

All write operations goes to primary

Automatic failover

Automatic Recovery

Consensus election of primary

Set up a replica set In this tutorial we will convert standalone mongod instance to a replica set. To convert to replica set follow the below given steps:

Shutdown already running mongodb server.

Now start the mongodb server by specifying --replSet option. Basic syntax of --replSet is given below:

mongod --port "PORT" --dbpath "YOUR_DB_DATA_PATH" --replSet "REPLICA_SET_INSTANCE_NAME"

Example

mongod --port 27017 --dbpath "D:\set up\mongodb\data" --replSet rs0

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It will start a mongod instance with the name rs0, on port 27017. Now start the command prompt and connect to this mongod instance. In mongo client issue the command rs.initiate() to initiate a new replica set. To check the replica set configuration issue the command rs.conf(). To check the status of replica sete issue the command rs.status().

Add members to replica set To add members to replica set, start mongod instances on multiple machines. Now start a mongo client and issue a command rs.add().

Synttax:

Basic syntax of rs.add() command is as follows:

>rs.add(HOST_NAME:PORT)

Example

Suppose your mongod instance name is mongod1.net and it is running on port 27017. To add this instance to replica set issue the command rs.add() in mongo client.

>rs.add("mongod1.net:27017")

>

You can add mongod instance to replica set only when you are connected to primary node. To check whether you are connected to primary or not issue the command db.isMaster() in mongo client.

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MongoDB Sharding

Sharding Sharding is the process of storing data records across multiple machines and it is MongoDB's approach to meeting the demands of data growth. As the size of the data increases, a single machine may not be sufficient to store the data nor provide an acceptable read and write throughput. Sharding solves the problem with horizontal scaling. With sharding, you add more machines to support data growth and the demands of read and write operations.

Why Sharding? In replication all writes go to master node

Latency sensitive queries still go to master

Single replica set has limitation of 12 nodes

Memory can't be large enough when active dataset is big

Local Disk is not big enough

Vertical scaling is too expensive

Sharding in MongoDB Below given diagram shows the sharding in MongoDB using sharded cluster.

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In the above given diagram there are three main components which are described below:

Shards: Shards are used to store data. They provide high availability and data consistency. In production

environment each shard is a separate replica set.

Config Servers: Config servers store the cluster's metadata. This data contains a mapping of the cluster's data

set to the shards. The query router uses this metadata to target operations to specific shards. In production

environment sharded clusters have exactly 3 config servers.

Query Routers: Query Routers are basically mongos instances, interface with client applications and direct

operations to the appropriate shard. The query router processes and targets operations to shards and then

returns results to the clients. A sharded cluster can contain more than one query router to divide the client request

load. A client sends requests to one query router. Generally a sharded cluster have many query routers.

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MongoDB Create Backup

Dump MongoDB Data To create backup of database in mongodb you should use mongodump command. This command will dump all data

of your server into dump directory. There are many options available by which you can limit the amount of data or create backup of your remote server.

Syntax:

Basic syntax of mongodump command is as follows

>mongodump

Example

Start your mongod server. Assuming that your mongod server is running on localhost and port 27017. Now open a command prompt and go to bin directory of your mongodb instance and type the command mongodump


>mongodump

The command will connect to the server running at 127.0.0.1 and port 27017 and back all data of the server to directory /bin/dump/. Output of the command is shown below:

There are a list of available options that can be used with the mongodump command.

This command will backup only specified database at specified path

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Syntax Description Example

mongodump --host HOST_NAME –port PORT_NUMBER

This commmand will backup all databases of specified mongod instance.

mongodump --host tutorialspoint.com – port 27017

mongodump --dbpath DB_PATH --out BACKUP_DIRECTORY

mongodump --dbpath /data/db/ --out /data/backup/

mongodump --collection COLLECTION --db DB_NAME

This command will backup only specified collection of specified database.

mongodump --collection mycol --db test

Restore data To restore backup data mongodb's mongorerstore command is used. This command restore all of the data from the

back up directory.

Syntax

Basic syntax of mongorestore command is

>mongorestore

Output of the command is shown below:

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MongoDB Deployment

When you are preparing a MongoDB deployment, you should try to understand how your application is going

to hold up in production. It’s a good idea to develop a consistent, repeatable approach to managing your deployment environment so that you can minimize any surprises once you’re in production.

The best approach incorporates prototyping your set up, conducting load testing, monitoring key metrics, and using that information to scale your set up. The key part of the approach is to proactively monitor your entire system - this will help you understand how your production system will hold up before deploying, and determine where you will need to add capacity. Having insight into potential spikes in your memory usage, for example, could help put out a write-lock fire before it starts.

To monitor your deployment MongoDB provides some commands that are shown below:

mongostat This command checks the status of all running mongod instances and return counters of database operations. These counters include inserts, queries, updates, deletes, and cursors. Command also shows when you’re hitting page faults, and showcase your lock percentage. This means that you're running low on memory, hitting write capacity or have some performance issue.

To run the command start your mongod instance. In another command prompt go to bin directory of your mongodb installation and type mongostat.

D:\set up\mongodb\bin>mongostat


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mongotop This command track and report the read and write activity of MongoDB instance on a collection basis. By default mongotop returns information in each second, by you can change it accordingly. You should check that this read

and write activity matches your application intention, and you’re not firing too many writes to the database at a time, reading too frequently from disk, or are exceeding your working set size.

To run the command start your mongod instance. In another command prompt go to bin directory of your mongodb installation and type mongotop.

D:\set up\mongodb\bin>mongotop


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To change mongotop command to return information less frequently specify a specific number after the mongotop

command.

D:\set up\mongodb\bin>mongotop 30

The above example will return values every 30 seconds.

Apart from the mongodb tools, 10gen provides a free, hosted monitoring service MongoDB Management Service (MMS), that provides a dashboard and gives you a view of the metrics from your entire cluster.

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MongoDB Java

Installation Before we start using MongoDB in our Java programs, we need to make sure that we have MongoDB JDBC Driver and Java set up on the machine. You can check Java tutorial for Java installation on your machine. Now, let us check how to set up MongoDB JDBC driver.

You need to download the jar from the path Download mongo.jar. Make sure to download latest release of it.

You need to include the mongo.jar into your classpath.

Connect to database To connect database, you need to specify database name, if database doesn't exist then mongodb creates it automatically.

Code snippets to connect to database would be as follows:

import com.mongodb.MongoClient;

import com.mongodb.MongoException;

import com.mongodb.WriteConcern;

import com.mongodb.DB;

import com.mongodb.DBCollection;

import com.mongodb.BasicDBObject;

import com.mongodb.DBObject;

import com.mongodb.DBCursor;

import com.mongodb.ServerAddress;

import java.util.Arrays;

public class MongoDBJDBC{

public static void main( String args[] ){

try{

// To connect to mongodb server

MongoClient mongoClient = new MongoClient( "localhost" , 27017 );

// Now connect to your databases

DB db = mongoClient.getDB( "test" );

System.out.println("Connect to database successfully");

boolean auth = db.authenticate(myUserName, myPassword);

System.out.println("Authentication: "+auth);

}catch(Exception e){

System.err.println( e.getClass().getName() + ": " + e.getMessage() );

}

}

}

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Now, let's compile and run above program to create our database test. You can change your path as per your requirement. We are assuming current version of JDBC driver mongo-2.10.1.jar is available in the current path

$javac MongoDBJDBC.java

$java -classpath ".:mongo-2.10.1.jar" MongoDBJDBC

Connect to database successfully

Authentication: true

If you are going to use Windows machine, then you can compile and run your code as follows:

$javac MongoDBJDBC.java

$java -classpath ".;mongo-2.10.1.jar" MongoDBJDBC



Value of auth will be true, if the user name and password are valid for the selected database.

Create a collection To create a collection, createCollection() method of com.mongodb.DB class is used.

Code snippets to create a collection:











public class MongoDBJDBC{ public static void main( String args[] ){

try{








DBCollection coll = db.createCollection("mycol");

System.out.println("Collection created successfully");



}

}

}

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When program is compiled and executed, it will produce the following result::



Collection created successfully

Getting/ selecting a collection To get/select a collection from the database, getCollection() method of com.mongodb.DBCollection class is used.

Code snippets to get/select a collection:













try{








DBCollection coll = db.createCollection("mycol");

System.out.println("Collection created successfully");

DBCollection coll = db.getCollection("mycol");

System.out.println("Collection mycol selected successfully");



}

}

}

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Collection created successfully

Collection mycol selected successfully

Insert a document To insert a document into mongodb, insert() method of com.mongodb.DBCollection class is used.

Code snippets to insert a documents :













try{










BasicDBObject doc = new BasicDBObject("title", "MongoDB").

append("description", "database").

append("likes", 100).

append("url", "http://www.tutorialspoint.com/mongodb/").

append("by", "tutorials point");

coll.insert(doc);

System.out.println("Document inserted successfully");



}

}

}

When program is compiled and executed, it will produce the following result: :

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Document inserted successfully

Retrieve all documents To select all documents from the collection, find() method of com.mongodb.DBCollection class is used. This

method returns a cursor, so you need to iterate this cursor.

Code snippets to select all documents:













try{










DBCursor cursor = coll.find();

int i=1;

while (cursor.hasNext()) {

System.out.println("Inserted Document: "+i);

System.out.println(cursor.next());

i++;

}



}

}

}


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Inserted Document: 1

{

"_id" : ObjectId(7df78ad8902c),

"title": "MongoDB",

"description": "database",

"likes": 100,

"url": "http://www.tutorialspoint.com/mongodb/",

"by": "tutorials point"

}

Update document To update document from the collection, update() method of com.mongodb.DBCollection class is used.

Code snippets to select first document:













try{










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DBObject updateDocument = cursor.next();

updateDocument.put("likes","200")

col1.update(updateDocument);

}

System.out.println("Document updated successfully");

cursor = coll.find();

int i=1;


System.out.println("Updated Document: "+i);


i++;

}



}

}

}

When program is compiled and executed, it will produce the following result:




Document updated successfully

Updated Document: 1

{

"_id" : ObjectId(7df78ad8902c),

"title": "MongoDB",

"description": "database",

"likes": 100,

"url": "http://www.tutorialspoint.com/mongodb/",

"by": "tutorials point"

}

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Delete first document To delete first document from the collection, you need to first select the documents using findOne() method and then remove method of com.mongodb.DBCollection class.

Code snippets to delete first document:













try{










DBObject myDoc = coll.findOne();

col1.remove(myDoc);


int i=1;


System.out.println("Inserted Document: "+i);


i++;

} System.out.println("Document deleted successfully"); }catch(Exception e){ System.err.println( e.getClass().getName() + ": " + e.getMessage() ); } } }

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Document deleted successfully

Remaining mongodb methods save(), limit(), skip(), sort() etc works same as explained in subsequent

tutorial.

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MongoDB PHP

To use mongodb with php you need to use mongodb php driver. Download the driver from the url Download

PHP Driver. Make sure to download latest release of it. Now unzip the archive and put php_mongo.dll in your PHP

extension directory ("ext" by default) and add the following line to your php.ini file:

extension=php_mongo.dll

Make a connection and Select a database To make a connection, you need to specify database name, if database doesn't exist then mongodb creates it automatically.

Code snippets to connect to database would be as follows:

<?php

// connect to mongodb

$m = new MongoClient();

echo "Connection to database successfully";

// select a database

$db = $m->mydb;

echo "Database mydb selected";

?>

When program is executed, it will produce the following result::

Connection to database successfully

Database mydb selected

Create a collection Code snippets to create a collection would be as follows:

<?php

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https://s3.amazonaws.com/drivers.mongodb.org/php/index.html

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$db = $m->mydb;


$collection = $db->createCollection("mycol");

echo "Collection created succsessfully";

?>

When program is executed, it will produce the following result: :



Collection created succsessfully

Insert a document To insert a document into mongodb, insert() method is used.

Code snippets to insert a documents :

<?php





$db = $m->mydb;


$collection = $db->mycol;

echo "Collection selected succsessfully";

$document = array(

"title" => "MongoDB",

"description" => "database",

"likes" => 100,

"url" => "http://www.tutorialspoint.com/mongodb/",

"by", "tutorials point"

);

$collection->insert($document);

echo "Document inserted successfully";

?>

When program is executed, it will produce the following result::

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Collection selected succsessfully

Document inserted successfully

Find all documents

To select all documents from the collection, find() method is used.

Code snippets to select all documents:

<?php





$db = $m->mydb;




$cursor = $collection->find();

// iterate cursor to display title of documents

foreach ($cursor as $document) {

echo $document["title"] . "\n";

}

?>

When program is executed, it will produce the following result:




{

"title": "MongoDB"

}

Update a document To update a document , you need to use update() method.

In the below given example we will update the title of inserted document to MongoDB Tutorial. Code snippets to

update a document:

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<?php





$db = $m->mydb;




// now update the document

$collection->update(array("title"=>"MongoDB"), array('$set'=>array("title"=>"MongoDB Tutorial")));

echo "Document updated successfully";

// now display the updated document



echo "Updated document";



}

?>

When program is executed, it will produce the following result:




Document updated successfully

Updated document

{

"title": "MongoDB Tutorial"

}

Delete a document To delete a document , you need to use remove() method.

In the below given example we will remove the documents that has title MongoDB Tutorial. Code snippets to delete

document:

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<?php





$db = $m->mydb;




// now remove the document

$collection->remove(array("title"=>"MongoDB Tutorial"),false);

echo "Documents deleted successfully";

// now display the available documents



echo "Updated document";



}

?>

When program is executed, it will produce the following result: :




Documents deleted successfully

In the above given example second parameter is boolean type and used for justOne field of remove() method.

Remaining mongodb methods findOne(), save(), limit(), skip(), sort() etc works same as explained in above tutorial.